Ultra‐Thin Lead Sulfide Capping for Stabilizing Tin Halide Perovskite Solar Cells

Addressing the inherent instability of tin‐based perovskite solar cells (PSCs), a facile approach is introduced to simultaneously enhance their stability and performance. This study demonstrates the implementation of an ultra‐thin (≈3 nm) dual‐functional lead sulfide (PbS) capping layer, formed via a sequential deposition. This PbS layer serves a critical dual role: first, as a robust protective barrier against oxidation and moisture, effectively mitigating the degradation of the underlying tin‐based perovskite; and second, by improving interfacial electronic properties to facilitate efficient charge extraction. Specifically, the PbS layer not only provides conformal coverage and minimizes non‐radiative recombination but also acts as an n‐type interfacial layer, promoting electron transport. This synergistic effect results in a significant boost in power conversion efficiency (PCE) from 12.0% to 14.4% with an open‐circuit voltage of 0.845 V, and exceptional long‐term stability with negligible PCE decay after 1600 h in a nitrogen environment. Operando grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurements corroborate enhanced structural stability under operating conditions. These findings establish the PbS capping layer as a practical, facile, and highly effective strategy for advancing stable and high‐performance tin‐based PSCs, paving the way for their viable application in sustainable photovoltaics.